The present invention relates to a device and a method for determining a magnetic field, in particular with respect to its intensity and direction in the immediate vicinity of a magnet surface.
Magnetic fields or magnetic field components that emerge orthogonally to magnet surfaces can be measured using Hall probes or magnetoresistors as sensors, since they are responsive to magnetic field components that are oriented perpendicularly to the sensor surface. However, the magnetic field components that run in parallel to the magnet surfaces may only be routinely measured by these sensors at relatively large intervals of xe2x80x9ctypicallyxe2x80x9d a few millimeters, since adjustment of the sensors may be required in a direction normal to the magnet surface.
Measuring methods and measuring sensors that function on the basis of the Hall effect are discussed, for example, in the essay xe2x80x9cNeue alternative Lxc3x6sungen fxc3xcr Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basisxe2x80x9d (New Alternative Solutions for Speed Sensors on a Magnetoresistive Basis in Motor Vehicles) from VDI report no. 509, 1984, VDI Publishers. Hall sensors for sensing fields directed tangentially to the magnet surface are also referred to in xe2x80x9cSensors and Materialsxe2x80x9d, 5, 2 (1992), pp. 91 through 101, MYU, Tokyo, and, in the essay included therein by M. Parajape, L. Ristic and W. Allegretto xe2x80x9cSimulation, Design and Fabrication of a Vertical Hall Device for Two Dimensional Magnetic Field Sensingxe2x80x9d.
In addition to the sensors based on the Hall effect, so-called AMR and GMR angular-position sensors, which are based on the so-called magnetoresistive effect (GMR=giant magneto resistance, AMR=anisotropic magneto resistance), can be used to measure a magnetic field component directed in parallel to the sensor surface.
Sensors of this kind, which are discussed, for example, in German Published Patent Application No. 195 43 562 and German Published Patent Application No. 44 08 078, may be essentially only sensitive, within their operative range, to the direction of the magnetic field to be measured and, only to a slight extent, to its intensity. At the same time, the measured amplitude of a sensor of this kind may be substantially temperature-dependent, which may lead to significant measuring errors. On the other hand, AMR or GMR angular-position sensors may exhibit an angular accuracy of about 0.50 (i.e., the measuring accuracy for determining the direction of an external magnetic field to be measured by the sensor). This angular measurement may be only negligibly temperature-dependent, in contrast to the intensity measurement.
At the same time, however, these sensors may have the advantage of also being able to be used, for example, in the direct proximity of the surface of a magnet that produces the magnetic field to be measured, i.e., typically at a distance of less than 1 mm. In this regard, reference is again made to xe2x80x9cNeue alternative Lxc3x6sungen fxc3xcr Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basisxe2x80x9d (New Alternative Solutions for Speed Sensors on a Magnetoresistive Basis in Motor Vehicles) from VDI report no. 509, 1984, VDI Publishers.
The functioning of AMR and GMR angular position sensors and their use for measuring magnetic fields is also referred to in Sensors and Actuators, A21-A23, xe2x80x9cA Thin Film Magnetoresistive Angle Detectorxe2x80x9d, 1990, pp. 795 through 798.
An exemplary embodiment and/or exemplary method in accordance with the present invention for determining a magnetic field is believed to have the advantage of allowing the determination of, for the most part, any magnetic fields whatsoever with respect to their intensity and direction, at a selected detection location. Particularly advantageous in this context is that magnetic fields or magnetic field components, which are directed in parallel to, or emerge from, the surface, for example, of a magnet producing these magnetic field components, can be measured very closely to the surface of this magnet.
Thus, as an auxiliary magnetic field required for measuring the magnetic field of interest, i.e., to be determined, one can initially use an arbitrarily produced auxiliary magnetic field, which, must be known, however, at least with respect to its intensity, preferably with respect to its intensity and direction. A Helmholtz coil pair may be advantageously suited for producing this auxiliary magnetic field. The center has a homogenous magnetic field, whose intensity and direction are known, and which can be adjusted in a defined and simple fashion, for example, by way of the coil current.
To detect the magnetic field resulting from the superimposing of the auxiliary magnetic field and the magnetic field to be measured, with respect to its direction, an AMR or GMR angular position sensor that may be commercially available, may be used.
In this context, a device, such as a coil having a defined and variable magnetic field that can be produced by the coil, is integrated at the same time in the AMR or GMR angular position sensor, to produce the auxiliary magnetic field, thereby eliminating the need for an external component, such as the mentioned Helmholtz coil pair.
Moreover, before commencing with the measurement of the magnetic field of interest (target magnetic field), that flows out, for example, from the surface of a magnet, the GMR or AMR angular position sensor used can be utilized for calibration or test measurements. This is done initially, in the absence of this magnet, in that the generated auxiliary magnet field is measured or calibrated by the GMR or AMR angular position sensor at the particular detection location, with respect to intensity, or with respect to intensity and direction, for various parameter adjustments, to produce the auxiliary magnetic field. Alternatively, to measure the auxiliary magnetic field, a Hall sensor can also be used, however. Thus, in the subsequent measurement of the magnetic field to be determined, for which then, for example, the magnet producing the magnetic field to be determined, is placed at the detection location in question, the auxiliary magnetic field is known in each case for the various parameter adjustments of the auxiliary magnetic field (for example of the coil current).
The magnetic field of interest is determined using the known auxiliary magnetic field, by calculating the magnetic field to be measured from the direction, measured at the detection location, of the resulting magnetic field produced from the superimposition of the auxiliary magnetic field and the magnetic field to be measured.
To this end, the direction of the resulting magnetic field is determined for at least two auxiliary magnetic fields, at the detection location with respect to their various auxiliary magnetic fields, and the magnetic field to be measured is calculated therefrom with respect to its intensity and direction, employing any suitably appropriate numerical adaptation method, which in one exemplary embodiment is carried out or performed with the assistance of a computer program. This numerical adaptation may be carried out to improve the numerical stability and the measuring accuracy using measuring data, from a multiplicity of determinations of the resulting magnetic field, given in each case various auxiliary fields. Furthermore, with respect to measuring accuracy and numerical considerations, it is believed to be beneficial for the auxiliary magnetic fields to be oriented in each case roughly perpendicularly to the assumed direction of the magnetic field to be measured.
The exemplary method according to the present invention may be suited for determining a magnetic field emerging from a surface of a magnet, as well as, in particular, for determining a magnetic field directed substantially in parallel to the surface of a magnet, in direct proximity to the surface of this magnet. It may be routinely employed, for example, in the quality testing of magnets.